Installation directory blender on a MAC
Usually, you download a compressed folder, extract it and put it into the Applications folder. There's no real installation involved since all data is stored inside this folder which can be stored anywhere. So on mac the directory of Blender is individual on each system. 

The actual executable can be found within the Blender.app application bundle. Right click, select Show Package Contents and navigate to Contents/MacOS/ where the unix executable can be found (if the executable is what you're looking for). You can now drag&amp;drop this file into the terminal to get the full path.

If the only purpose is to access blender from a program locally, this may suffice. If you plan to make your program available for others, some more steps would be involved like prompting the user to specify a path to blender.